The present invention relates to the inhibition of acetylation of a substrate by arylamine N-acetyl transferase.
The majority of drugs are metabolized by enzymes in the body. Since many patients are simultaneously treated with two or more drugs, there is always the potential that one drug may interfere with the metabolism of another drug, e.g., one may inhibit the enzyme which transforms another. Inhibition of the metabolism of one drug by another drug is normally problematic. Metabolic drug-drug interactions can produce adverse reactions and nearly always require adjustments of doses. Such situations are nuisances and are desirably avoided.
Information on drug metabolism varies from one class of enzymes to another. For some drug-metabolizing enzymes (e.g., the cytochrome P450), literature on drugxe2x80x94drug interactions is voluminous. In contrast, very little has been reported for the arylamine N-acetyl transferases (NAT), i.e., enzymes which acetylate arylamine groups.
Unlike the wide variety of forms for cytochrome P450 and UDP-glucuronyl transferases, there are only two forms of human arylamine N-acetyl transferase, namely, NAT-1 and NAT-2. The level of expression varies substantially among individuals for both NAT-1 and NAT-2. NAT-2 is strongly polymorphic; indeed, it was the first enzyme for which polymorphism in human drug metabolism was appreciated. Among various ethnic populations, 30-80% of individuals are xe2x80x9cfastxe2x80x9d acetylators via NAT-2, and the remainder are xe2x80x9cslowxe2x80x9d acetylators. The polymorphism of NAT-1 has only recently been appreciated.
Others have described N-acetyl transferases which do not play a role in enzyme metabolism. For example, Hillman et al. (U.S. Pat. No. 5,795,724) disclose an N-acetyl transferase (NACTH) responsible for histone acetylation. NACTH differs from NAT in biological function and location in the cell. NACTH acts upon an entirely different family of substrates than NAT. In addition, NACTH is found in the nucleus of the cell, whereas NAT is located in the cytoplasm.
A number of compounds are known in the art which have arylamine groups that can be acetylated by NAT. For example, para-amino-benzoic acid (PABA), para-amino-salicylate (PAS) and sulfamethoxazole (SMX) are acetylated by NAT-1. PABA is well-known as a topical sunscreen. PAS is used for the therapy of tuberculosis, but even with the recent increase in tuberculosis, incidence of tuberculosis is still rare, and there are other more active drugs. SMX is commonly prescribed for the treatment of infections in the urinary tract and elsewhere. Drugs identified as being acetylated by NAT-2 are numerous and include isoniazid (INH), dapsone (DDS), sulphamethazine (SMZ), aminoglutethimide (AG), procainamide, and hydralazine.
Occasionally, situations arise in which it is desirable to inhibit the activity of a drug-metabolizing enzyme. Such situations include stretching a scarce or expensive supply of drugs (e.g., cyclosporin/ketoconazole), prolonging the half-life of an active drug to reduce the frequency of administration (e.g., AZT/probenecid), and blocking formation of a toxic metabolite (e.g., in cases of methanol poisoning, the use of ethanol to prevent formation of formaldehyde as a metabolite of methanol).
Oftentimes for NAT, it is desirable to inhibit the formation of a toxic metabolite. In some cases, the acetylated metabolite generated by NAT has been shown definitively to be more toxic than the parent drug. In other cases, there is not a direct link to a specific metabolite, but there is a strong association between high rates of acetylation and adverse reactions. As an extension of this category, even in the absence of drug therapy, there have been several linkages reported between acetylation rates and predisposition to diseases such as cancer. In certain situations, individuals with rapid acetylation have a 10-fold (or greater) risk of disease than individuals with slow acetylation (Lang et al. Environmental Health Perspectives 105(suppl. 4): 763-766 (1997)). For these situations, inhibition of NAT would be beneficial to patients.
Therefore, there exists a need for a method of inhibiting the acetylation of a substrate by NAT. The present invention seeks to provide such a method, as well as a composition for use in such a method. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The present invention is directed to a method of inhibiting arylamine N-acetyl transferase (NAT) from acetylating an arylamine group in a substrate. The method comprises contacting NAT with an inhibitor that interacts with NAT and thereby inhibits NAT from acetylating the arylamine group in the substrate. Preferably, the inhibitor of NAT is a compound of formula: 
wherein one or more carbon atoms at positions 2, 3, 5 and 6 can be heteroatoms, which can be the same or different and can be selected from the group consisting of oxygen, nitrogen and sulfur, R1 is one or more substituents, which can be the same or different, selected from the group consisting of hydrogen, hydroxy, an alkoxy, sulfhydryl, nitro, amino, a halo, an aryloxy, cyano, xe2x80x94[SO2xe2x80x94R4], an alkyl, a cycloalkyl, a heterocycloalkyl, an alkenyl, an alkynyl, an aryl, a heteroaryl, an arylalkyl and a heteroarylalkyl, R2 is a substituent selected from the group consisting of amino, carboxyamide, sulfamide, xe2x80x94[NHxe2x80x94NH2], xe2x80x94[SO2xe2x80x94NHxe2x80x94NH2] and xe2x80x94[COxe2x80x94NHxe2x80x94NH2], and R3 is a substituent selected from the group consisting of hydrogen, hydroxy, an alkoxy, sulfhydryl, nitro, amino, a halo, an aryloxy, cyano, xe2x80x94[SO2xe2x80x94R4], an alkyl, a cycloalkyl, a heterocycloalkyl, an alkenyl, an alkynyl, an aryl, a heteroaryl, an arylalkyl, a heteroarylalkyl, wherein R4 is a substituent selected from the group consisting of hydrogen, hydroxy, an alkoxy, sulfhydryl, nitro, amino, a halo, an aryloxy, cyano, an alkyl, a cycloalkyl, a heterocycloalkyl, an alkenyl, an alkynyl, an aryl, a heteroaryl, an arylalkyl, a heteroarylalkyl, and NHxe2x80x94R5, wherein R5 is a substituent selected from the group consisting of hydrogen, hydroxy, an alkoxy, sulfhydryl, nitro, amino, a halo, an aryloxy, cyano, an alkyl, a cycloalkyl, a heterocycloalkyl, an alkenyl, an alkynyl, an aryl, a heteroaryl, an arylalkyl and a heteroarylalkyl, wherein the substituent is unsubstituted or substituted with one to three groups, which may be the same or different and are selected from the group consisting of an alkyl, an alkenyl, an alkynyl, xe2x95x90O, a halo, hydroxy, a lower alkoxy, carboxy, a carboalkoxy, a carboxamido, cyano, carbonyl, xe2x80x94NO2, an alkylthio, sulfoxide, sulfone, acylamino, amidino, an aryl, a heteroaryl, an aryloxy, and a heteroaryloxy.
The present invention also provides a composition comprising a compound comprising an arylamine group that can be acetylated by NAT and an inhibitor which interacts with NAT to inhibit NAT from acetylating the arylamine group in the compound.